Age dependent changes in the relative proportions of (a) elastin and collagen (b) amorphous and microfibrillar component of elastic tissue and (c) type I and III collagen will be determined. Specimen will be derived from human lung parenchyma of patients who died without overt disease or deterioration of the lung. Aliquots of crude connective tissue will be subjected to complete amino acid analysis and quantitative changes estimated from non-polar amino acid ratio, desmosine and isodesmosine content and hydroxyproline content. Qualitative differences will be assessed by analysis of isolated and purified elastin, microfibrillar glycoprotein and solubilized collagen. Morphological, biochemical and immunological parameters will be compared.